This is a renewal grant application for grant DA011946 in response to Program Announcement PA-02-085 (Neuroscience Research on Drug Addiction). Tobacco smoking, attributed at least partly to the addictive properties of nicotine, is a worldwide health problem that contributes to significant medical costs, deaths and human suffering. Research investigating the mechanisms of nicotine dependence will provide insights into the development of novel behavioral and pharmacological approaches to treat nicotine dependence and habitual tobacco smoking. During the previous funding period, the critical involvement of the glutamate system in both the reinforcing effects of nicotine and the development of nicotine dependence was shown. These data suggested that: a) decreasing glutamate transmission at postsynaptic metabotropic (mGluR) and ionotropic (iGluR) glutamate receptors decreases the reinforcing effects of nicotine;and b) during the development of nicotine dependence there are adaptations in glutamate system function, involving changes in the activity of pre- and post-synaptic glutamate receptors, to counteract the stimulatory effects of nicotine on glutamate transmission. The proposed work will extend these previous findings by investigating brain sites where glutamate plays a role in nicotine reinforcement and dependence. Specific Aim 1 will explore brain sites involved in glutamatergic regulation of intravenous nicotine self-administration in rats, by administering mGluR5, NMDA or AMPA/kainate receptor antagonists into the nucleus accumbens shell, the ventral tegmental area, the central nucleus of the amygdala or the prefrontal cortex. Specific Aim 2 will explore brain sites (same as in Aim 1) where adaptations in glutamate system function occur with the development of nicotine dependence, that affect the regulation of brain reward function in nicotine-dependent rats. Brain reward function will be assessed with the intracranial self-stimulation procedure. The focus will be on mGluR2/3 and AMPA/kainate receptors. Finally, Specific Aim 3 will study intravenous nicotine self-administration in mGluR2/3 and mGluR7 knockout mice to further explore the role of these glutamate receptors in nicotine reinforcement. This work will provide information about the role of glutamate transmission in specific brain sites in nicotine reinforcement, and reveal adaptations that occur in glutamate function in specific brain sites during nicotine dependence;these adaptations are likely to contribute to the affective aspects of nicotine withdrawal and lead to relapse. Such studies will identify novel therapeutic targets for the treatment of nicotine dependence and habitual tobacco smoking in humans.